Connectors are used to connect tubes for piping which have been heavily used in the industrial equipment to each other. Connectors with various kinds of structures capable of immobilizing tubes with respect to each other and ensuring the sealing performance at the connecting portion have been proposed. Among the structures associated with strong immobilizing means, those associated with a flange method, a screw-in method, a welding method, and the like have been in heavy usage. However, piping work is not efficient and potential leakage due to improper piping work can not be ignored either.
Thus, simplified connectors which do not require processes such as threading, welding, and the like and are adapted for a little eccentricity of tubes with respect to each other have been often used. In the simplified connector, with a rubber gasket and a retainer attached to each end of a sleeve member by means of coupling, the sealing at end potions of tubes is ensured by the elasticity of the rubber gaskets, and as-cut end portions of the tubes are connected to each other only through tightening the coupling. Furthermore, in some uses, the members are initially assembled into a single connector and then each end portion of the tubes is inserted into the single connector from both of the directions so as to connect the tubes to each other.
In the simplified connector described above, because the rubber gasket is forced to tightly contact with the tube only through tightening the coupling, the connected tube is allowed to move in the axial direction. And, if the tube moves and comes off, an internal fluid will leak. Then, if the internal fluid is hot or a hazardous chemical, it should be extremely dangerous and may lead to a serious disaster. Thus, in order to avoid such a disaster, a preventive arrangement for preventing the tube from coming off, such as always fixing the tube to a floor or a wall, is additionally required, resulting in increase in cost due to such construction.
Thus, as shown in FIG. 1, a grip ring 2, which is produced from spring steel made of stainless steel or steel and has wedge-shaped grooves 1 in the circumferential direction of the inner face thereof, has been used as one of the constitutional members for the tube connector. The tube connector having the grip rings has been disclosed in Published Japanese Translations of International Application Publication of Japanese Patent Application No. 2001-507782. It will be described with reference to FIG. 2. Referring now to FIG. 2, reference numeral 3 denotes a rotatable connecting piece, and reference numeral 4 denotes a fixed connecting piece. The grip ring 2 is tightly in contact with an inner face of the connecting piece 3, one end of the grip ring 2 is engaged in an engaging piece 5, and this engaging piece 5 is fixed through a fixing mechanism comprised of a bolt 6 and a nut 7. Furthermore, a rubber gasket 8 is tightly in contact with an inner face of the connecting piece 4. Inner diameters of the grip ring 2 and the rubber gasket 8 are formed to be slightly larger than an outer diameter of the tube to be inserted into this connector. If a tube is inserted into the tube connector from both sides, the bolt 6 is removed from the nut 7, and the engaging piece 5 is pulled out, then, in response to a spring action of the grip ring 2, wedge-shaped grooves 1 would bite into the tube and thereby inhibit the movement of the tube in the axial direction. Furthermore, the connecting piece 3 is turned around along an inner face of the connecting piece 4, and the connecting piece 3 and the connecting piece 4 are then tightly connected by means of the bolt 6 and the nut 7.
In this way, the use of the connector having the grip rings makes it possible to inhibit the movement of the tube in the axial direction and fix it tightly. These grip rings have been conventionally produced in the following way.
The producing method comprises the following steps: winding up metallic wire with predetermined shape; in a coil shape; cutting out a predetermined length of the metallic wire from the metallic wire wound in the coil shape; “bending” the cut-out portion of the metallic wire to be ring shaped; “welding” together both ends of the ring-shaped metallic wire so as to turn the blended metallic wire to be topic-shaped; performing “strain relieving annealing” to eliminate the thermal strain associated with the welding; performing “machine cutting” to provide wedge-shaped grooves on the inner face of the topic-shaped metallic wire in the circumferential direction by use of a lathe turning machine or the like; “cutting the welded portion” to obtain a ring piece which is a discrete entity from the topic-shaped metallic wire which is a continuous entity; and performing “cut treatment” on both ends of the ring piece to complete the work.
As described above, the conventional producing method of the grip rings requires many process steps. Furthermore, the steps of welding, annealing for relieving the strain, and cutting the welded portion are extra steps in view of forming the wedge-shaped grooves and hence not necessary. Another problem is that the material is not efficiently utilized because the welded portion is cut off. What is worse, there is a drawback that the value of finished products is lowered since the welding and the annealing for relieving the'strain cause the surface to be oxidized and discolored, leading to the deterioration of the surface quality. Thus, with the conventional producing method, increase in production cost can not be avoided and the grip rings with high-quality can not be provided either.
The present invention is directed to solve the problems described above, and an object thereof is to provide metallic wire for grip rings with high surface quality and low-cost. Furthermore, another object of the present invention is to provide a method for effectively producing metallic wire for grip rings. Even furthermore, another object of the present invention is to provide an apparatus suitable for producing metallic wire for grip rings. Furthermore, another object of the present invention is to provide a method for effectively producing grip rings for tube connectors using metallic wire. Even furthermore, another object of the present invention is to provide an apparatus suitable for producing the grip rings for tube connectors. Still furthermore, the other object of the present invention is to provide the grip ring with high surface quality and low-cost for tube connectors.